**1. Introduction**

Purple flesh sweet potato (*Ipomoea batatas*) is a very nutritious root vegetable native to the tropical regions of America. They are an abundant source of carbohydrates, dietary fiber, vitamins including A, B1, B2, C, and E, and minerals including Ca, Mg, K, and Zn [1]. In addition, purple flesh sweet potatoes (PFSP) contain a large amount of anthocyanins, an antioxidant whose long-term dietary intake can prevent cancer, cardiovascular diseases, viral infections, Alzheimer's disease, and diabetes [2]. The growing consciousness among consumers about what they eat, especially the health benefits, has led to an increase in the consumption of fruits and vegetables. Combined with busy lifestyle patterns, the demand for fresh-cut produce has increased significantly in recent years [3]. Ready-to-use fresh-cut produce is convenient, eliminates consumer waste, and saves time. However, the minimal processing of fresh-cut produce results in tissue softening and discoloration. It increases microbiological deterioration due to the exposed tissues, which makes them vulnerable to metabolism, microbial invasion, and mechanical damage [4]. These factors impact a product's storage and shelf life [5,6]. Therefore, a suitable packaging technique effective to reduce these factors influence and preserve the quality of fresh-cut produce during marketing and storage is required [4].

Antimicrobial coatings/films (inedible or edible) and modified atmosphere packaging (MAP) have been applied to fresh produce to maintain their qualities and extend their shelf life [7–10]. In particular, edible coatings have been investigated for their potential to

**Citation:** Chit, C.-S.; Olawuyi, I.F.; Park, J.J.; Lee, W.Y. Effect of Composite Chitosan/Sodium Alginate Gel Coatings on the Quality of Fresh-Cut Purple-Flesh Sweet Potato. *Gels* **2022**, *8*, 747. https:// doi.org/10.3390/gels8110747

Academic Editors: Aris E. Giannakas, Constantinos Salmas and Charalampos Proestos

Received: 31 October 2022 Accepted: 16 November 2022 Published: 17 November 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

enhance the quality and shelf life of food items [3,11]. Edible coatings can preserve fresh-cut food from mechanical and microbial damage, delay biochemical changes, and enhance their surface appearance [12]. Moreover, edible coatings can meet additional requirements, such as having antimicrobial activity and acting as good moisture and oxygen barriers. These requirements are beneficial for whole or fresh-cut fruits and vegetables that are often prone to microbial harm and highly susceptible to water loss, which causes size shrinkage and texture degradation [5]. Thus, coatings intended for fruit and vegetable preservation are expected to have good gas permeability for typical CO2/O<sup>2</sup> exchange, low water vapor permeability to minimize moisture leakage, and antibacterial properties to inhibit microbial proliferation. It is, however, challenging for a single coating material to satisfy all these requirements [13]

The composite layer-by-layer (LbL) coating technique, which is based on electrostatic deposition technology, was developed to incorporate numerous preservatives derived from various polymer components [5,14]. This approach is based on the alternate deposition of oppositely charged polyelectrolytes in the presence of a cross linking agent, resulting in a novel gel coating with improved properties and functionalities [11]. Due to the effectiveness of the LbL coating technique, its commercial implementation has been suggested for preserving minimally processed fruits. Cationic biopolymers such as chitosan and poly-L-lysine, and anionic biopolymers such as pectin and alginate are commonly used for LbL coating of foods [15]. Alginate is a hydrophilic biopolymer with excellent film-forming properties due to its unusual colloidal properties, including thickening, suspension formation, gel formation, and emulsion stabilization [16]. In addition, sodium alginate coating was beneficial in preserving the post-harvest quality of tomatoes [17] and peaches [18]. However, alginate has no antimicrobial properties, and their poor mechanical properties and water vapor resistance has limited their industrial applications [19]. In contrast, chitosan, a cationic polysaccharide with a high molecular weight and soluble in organic acids, is applicable as a preservative coating material for fruits due to its anti fungal mechanisms [20–23].

Some studies have examined the effect of alginate and chitosan on fresh-cut melon, mangoes, blueberries [24], guavas, and nectarines [25]. The combination of alginate and chitosan displayed various preservative effects depending on the fresh-cut fruit. However, the application of the sequential coating of chitosan and alginate on fresh-cut purple sweet potatoes has not been studied. This study aimed to investigate the effect of chitosan coating (Ch), sodium alginate gel coating (SA + C), and their composite gel coating (ChCSA) on the quality and shelf life of fresh-cut purple sweet potatoes during refrigerated storage at 5 ◦C for 16 days.
